Method of determining at least one parameter of visual behaviour of an individual

ABSTRACT

Disclosed is a method of determining at least one visual behavior parameter of an individual, including: determination of the position of the center of rotation of at least one eye of the individual in a first reference frame tied to the head of the individual; capture, with the aid of an image capture device, of at least one image of at least one part of the body of the individual in a second reference frame, determination of the position and the orientation, in the second reference frame, of the first reference frame tied to the head of the individual, by searching for the position, in the second reference frame of a distinctive zone of the part of the body of the individual; determination of the position of the center of rotation of the eye in the second reference frame; and determination of the sought-after visual behavior parameter.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of personalization ofophthalmic lenses intended to be fitted in a spectacle frame.

It more precisely relates to a method for determining at least oneparameter of visual behavior of an individual.

PRIOR ART

Methods allowing the ophthalmic lenses of a piece of optical equipmentintended for an individual to be personalized depending on parametersassociated with the individual and the spectacle frame chosen therebyare known.

Such a method is for example based on the determination of the positionof the rotation center of each eye of the individual with respect to theframe positioned on his head. It is then possible to precisely determinethe position of the optical center of each ophthalmic lens in the chosenframe so that the ophthalmic lens is correctly positioned in front ofthe eyes of the individual.

Here, the position of the rotation center of the eye is determined withrespect to the ophthalmic lens, statically, under conditions that arevery different from the natural conditions under which the frame isworn, without taking into account the posture of the individual.

Known methods do not allow, for example, the position of the rotationcenter of the eye of the individual to be determined with respect to theposture of the body of the individual, under conditions similar to thoseencountered in the day-to-day life of the individual and possibly duringa movement of this individual.

Specifically, existing methods and devices that allow the posture of thebody to be determined with respect to the image-capturing device are notprecise enough to allow the position of the rotation centers of the eyesto be determined with respect to the body.

SUBJECT OF THE INVENTION

In order to remedy the aforementioned drawbacks of the prior art, thepresent invention proposes a method for determining at least oneparameter of visual behavior of an individual allowing the posture ofthe body of the individual to be taken into account.

More particularly, according to the invention a method for determiningat least one parameter of visual behavior of an individual is proposed,this method comprising the following steps:

-   -   determining the position of the rotation center of at least one        eye of the individual in a first frame of reference associated        with the head of the individual,    -   capturing, using an image-capturing device, at least one image        of at least one portion of the body of the individual in a        second frame of reference,    -   determining the position and orientation, in the second frame of        reference, of the first frame of reference associated with the        head of the individual, by seeking the position, in the second        frame of reference, of a recognizable zone of said portion of        the body of the individual,    -   determining the position of the rotation center of the eye in        the second frame of reference,    -   determining the sought parameter of visual behavior.

It is thus possible to personalize the ophthalmic lenses intended forthe spectacle frame chosen by this individual depending on thisparameter of visual behavior.

It will be noted that the parameter of visual behavior is determined inthe second frame of reference, for example in a context in which theindividual is behaving more naturally; this determination may howeverthus use the position of the rotation center of the eye (in the secondframe of reference) initially determined with precision in the firstframe of reference, for example in a professional environment.

For the capturing step, the individual is for example placed in areal-life situation in which the posture of the head and body of theindividual is unconstrained.

The parameter of visual behavior is thus determined, while taking intoaccount the position of the rotation center of the eye, in the secondframe of reference in which the posture of the head and the body of theindividual correspond to that which he adopts naturally, in thereal-life situation in question.

Moreover, the position and/or orientation of the recognizable zone ofsaid portion of the body of the individual are for example predeterminedin the first frame of reference, thereby allowing, on the basis of theimage captured in the second frame of reference, the relative positionof the first frame of reference and the second frame of reference to beobtained.

The following are other nonlimiting and advantageous features of themethod according to the invention:

-   -   in the step of determining the position of the rotation center        in the first frame of reference, the position of the rotation        center of the eye of the individual is determined from a        morphological database of the individual;    -   in the step of determining the position of the rotation center        in the first frame of reference, the position of the rotation        center of the eye of the individual is determined from one or        more acquisitions of images of the head of the individual;    -   in the capturing step, said image is a three-dimensional        representation of the portion of the body of the individual or        of the head of the individual;    -   in the capturing step, a sequence of images is preferably        captured during a predetermined duration, and, in the step of        determining the sought parameter of visual behavior, the        variation in the sought parameter of visual behavior during this        predetermined duration is deduced therefrom;    -   in the capturing step, at least one sequence of ten images is        captured while the movements of the individual are        unconstrained;    -   in the step of determining position and orientation, said        recognizable zone consists of a pinpointing device mounted on        the head of the individual, of a spectacle frame placed on the        head or of one or more recognizable points of the face of the        individual;    -   in the step of determining the sought parameter of visual        behavior, the direction of the gaze of the individual in said        real-life situation is determined, and a zone of use of the        ophthalmic lens corresponding to this real-life situation is        determined therefrom;    -   to determine the direction of the gaze of the individual, the        image of the pupil of the individual is identified in the image        captured in the capturing step, and the sought direction of the        gaze is deduced therefrom depending on the position of the        rotation center in the first frame of reference, said position        being determined in the step of determining the position of the        rotation center in the first frame of reference;    -   to determine the direction of the gaze of the individual, the        position in the second frame of reference of elements targeted        by the gaze and belonging to the environment of the individual        is determined;    -   said elements targeted by the gaze are displayed on an        electronic screen and have a known position with respect to the        image-capturing device;    -   in the step of determining the position of the rotation center        in the first frame of reference,        -   at least two images of the head of the individual are            captured using an image-capturing device, in which images            the postures of the head of the individual with respect to            this image-capturing device are different and in which            images the individual is fixating his gaze on a sighting            point of predetermined position,        -   the gaze directions of the individual corresponding to each            of the two images are determined,        -   the position of the rotation center of the eye of the            individual is deduced therefrom;    -   the aforementioned real-life situation is one of the following        real-life situations:        -   reading and/or writing situations,        -   rest situations,        -   walking on foot situations,            -   situations in which the individual is climbing or                descending a staircase;    -   in the capturing step, the image-capturing device is placed such        that the moving individual retains a substantially three-quarter        orientation with respect to this image-capturing device in the        corresponding real-life situation;    -   in the step of determining the position of the rotation center        in the first frame of reference, the head of the individual is        equipped with a pair of spectacles surmounted by a pinpointing        system, in the capturing step, the captured portion of the body        comprises the head of the individual equipped with this        pinpointing system, and, in the step of determining the position        and orientation, the recognizable zone consists of this        pinpointing system;    -   the sought parameter of visual behavior of the individual is one        of the following:        -   a zone of use corresponding to the real-life situation for a            corrective lens to be placed in a spectacle frame intended            to equip the head of the individual,            -   a behavioral parameter of the individual specifying                whether he moves his eyes or head more,        -   average reading distance,        -   natural posture of the individual at rest,        -   dynamic behavior of the eyes during the chosen real-life            situation,        -   position of a near-vision zone or progression length or            inset of a corrective lens to be placed in a spectacle frame            intended to equip the head of the individual,        -   the pantoscopic angle of a corrective lens to be placed in a            spectacle frame intended to equip the head of the individual            determined so as to decrease the astigmatic aberrations;    -   the steps of determining the position of the rotation center in        the first frame of reference and of capturing are carried out in        one and the same place, using one and the same image-capturing        device;    -   the steps of determining the position of the rotation center in        the first frame of reference and of capturing are carried out in        two different places, using two different image-capturing        devices;    -   at least the capturing step is carried out by the individual in        his usual environment.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The description which follows with regard to the appended drawings,given by way of nonlimiting examples, will clearly elucidate the gist ofthe invention and how it may be embodied.

In the appended drawings:

FIG. 1 is a schematic profile view of the head of the individual duringan image capture in step a) of the method according to the invention,and

FIG. 2 is a schematic view of the body of the individual during an imagecapture in step c) of the method according to the invention.

The method according to the invention includes the following steps:

a) the position of the rotation center of at least one eye of theindividual in a first frame of reference associated with the head of theindividual is determined,

b) the individual is placed in a real-life situation in which theposture of the head and body of the individual is unconstrained,

c) at least one image of at least one portion of the body of theindividual is captured using an image-capturing device,

d) depending on the image captured in step c), the position andorientation of said portion of the body of the individual is determinedin a second frame of reference,

e) the position and orientation, in the second frame of reference, ofthe first frame of reference associated with the head of the individualis determined by seeking the position, in the second frame of reference,of a recognizable zone of said portion of the body of the individual,the position and orientation of which in the first frame of referenceare predetermined,

f) the position of the rotation center of the eye in the second frame ofreference are deduced therefrom,

g) the sought parameter of visual behavior is deduced therefrom.

In practice, the method is implemented by a computational processingunit.

This computational processing unit makes use of the position of therotation center of at least one eye of the individual in the first frameof reference associated with the head of the individual, which positionis present in a memory of this processing unit and transmitted to thisprocessing unit or indeed determined by the processing unit frommeasurements carried out on the individual, especially two-dimensionalor three-dimensional images of the head of this individual captured instep a) by a first device for capturing two-dimensional orthree-dimensional images.

It also makes use of other measurements carried out on the individual,comprising at least one two-dimensional or three-dimensional image of aportion of the body of the individual, said image being captured in stepc) with a second image-capturing device that may be the same as thatused possibly in step a).

By portion of the body, what is meant is a portion of the bodycomprising at least one portion other than the head of the individual.More precisely, it is preferably a question of a portion of the bodylocated below the shoulder line of the individual.

This portion of the body may include the head of the individual. Itfurthermore preferably includes the neck and/or a portion of the chestof the individual.

It may include all of the body and head of the individual, as explainedbelow.

From the two- or three-dimensional images obtained in step c), thecomputational processing unit determines the posture of said portion ofthe body in the second frame of reference, i.e. the position andorientation of this portion of the body in the second frame ofreference.

This second frame of reference may be a frame of reference associatedwith the image-capturing device or an absolute spatial frame ofreference, or a frame of reference associated with an element of theenvironment of the individual.

Next, the computational processing unit is programmed to reposition thefirst frame of reference associated with the head of the individual withrespect to the second frame of reference, so as to allow the position ofthe rotation centers of the eyes of the individual with respect to theportion of the body of the individual to be determined.

The computational processing unit then deduces therefrom at least oneparameter of visual behavior of the individual. By virtue of thepreceding steps, this determination takes into account the posture ofthe body and of the head of the individual in its real-life situation.

The various steps will now be described in more detail.

Step a)

In this step, the position of the rotation center CRO of at least oneeye OD of the individual is determined in the first frame of referenceassociated with the head TS of the individual, by any technique known tothose skilled in the art.

The head of the individual TS is for example shown in FIG. 1.

The Frankfurt plane PF of the head TS of the individual is defined asthe plane passing through the lower orbital points OR and the porion POof the individual, the porion being the highest point in the skull ofthe auditory canal, which corresponds to the tragion of the ear.

The Frankfurt plane PF is horizontal in an orthostatic position, inwhich position he makes a minimum of effort. The gaze axis of theindividual is then the primary gaze axis, i.e. he is gazing straightahead.

A sagittal plane PSAG of the head TS of the individual is defined asbeing the vertical plane passing through the perpendicular bisector ofthe two eyes. The perpendicular bisector of the eyes is the axis passingthrough the middle of the segment defined by the rotation centers of thetwo eyes, perpendicular to this segment, and parallel to the Frankfurtplane PF.

Preferably, this rotation center is determined from a measurementcarried out on the face of the individual.

This measurement may especially comprise capturing one or moretwo-dimensional images of the head of the individual or acquiring one ormore three-dimensional representations of the head of the individual byvirtue of a first image-capturing device.

It is here preferably a question of capturing an image or acquiring arepresentation having a high resolution, for example at least 640×480(VGA).

Thus, according to a first embodiment of step a), the position of therotation center CRO of the eye is determined from two two-dimensionalimages of the head of the individual in two different cephalic posturesfor one given gaze direction with respect to the first image-capturingdevice used to capture these images.

The principle of this determination is for example described in detailin document FR2914173, an equivalent of which in English is the documentUS20100128220.

In particular, according to this first embodiment of step a),

-   -   at least two images of the head of the individual are captured        using the first image-capturing device, in which images the        postures of the head of the individual with respect to the first        image-capturing device are different and in which images the        individual is fixating his gaze on a sighting point of        predetermined and fixed position,    -   the gaze directions of the individual corresponding to each of        the two images are determined,    -   the position of the rotation center of the eye of the individual        in the first frame of reference associated with the head of the        individual is deduced therefrom.

The captured images of the head of the individual are transmitted to thecomputational processing unit.

The captured images may be processed in real-time or after all theimages have been captured.

From these images captured in step a), the computational processing unitdetermines the position of the rotation center CRO of at least one eyeof the individual in the first frame of reference associated with thehead of the individual.

By way of example, it is possible to identify the images of arecognizable point of the eye of the individual, for example the pupilof the eye of the individual, in two images captured while theindividual is fixating his eyes on a target the position of which withrespect to the first image-capturing device is different for eachcaptured image.

The position of the target fixated with the gaze during the two imagecaptures being known relative to the first image-capturing device, theposition of the eye rotation center CRO is deduced therefrom as beingthe intersection of the straight lines passing through the target andthe pupil of the eye for each captured image.

It is also possible to determine for each gaze direction, thecorresponding posture of the head of the individual, i.e. its positionand its orientation in a frame of reference associated with the firstimage-capturing device. A data pair associating the posture of the headand the gaze direction is stored in correspondence with the image.

In practice, the first image-capturing device is then preferably acamera or video camera. It is for example securely fastened to a displayscreen on which said targets forming the sighting points are displayed.It may for example be a question of a tablet including a video camerathat constitutes the first image-capturing device. The targets maycomprise either a plurality of static images appearing at variouslocations on the screen, or a dynamic image moving across the screen.

The individual may optionally be equipped with a spectacle frame 10and/or a pinpointing system 40 intended to allow the position of thehead of the individual in space to be determined from a captured imageof the head of the individual equipped with the pinpointing system. Thispinpointing system is described in detail in document FR2914173, page 7,line 5 to page 10, line 8. It will therefore not be described in moredetail here.

The frame 10 may be full-rimmed or rimless. In the example shown in FIG.1, it is full-rimmed and therefore includes two rims 12 connected by abridge and intended to accommodate the ophthalmic lenses, and two frametemples 15 that are intended to rest on the ears of the individual.

The pinpointing system 40 has predetermined geometric characteristics,which allow, from a captured image of the head of the individual, inwhich image this pinpointing system appears, the position and theorientation of the head of the individual in space to be determined insaid frame of reference associated with the image-capturing device. Thispinpointing system therefore allows the position and orientation of thefirst frame of reference associated with the head of the individual tobe determined in the frame of reference associated with theimage-capturing device.

The first frame of reference (O1, X1, Y1, Z1) associated with the headof the individual may moreover be associated with the pinpointing system40, as schematically shown in FIG. 1. In this example, the center of theframe of reference is placed in the middle of the pinpointing system,which is located in the sagittal plane of the head of the individual.The axis (O1,Y1) extends in the midplane of the frame PM, which is herecoincident with the midplane of each rim PMC.

The axis (O1, X1) is parallel to the segment connecting the rotationcenters of the eyes of the individual and the axis (O1, Z1) isperpendicular to the two axes (O1, X1) and (O1, Y1).

The geometric characteristics of the pinpointing system 40 give accessto a scale factor of each captured image and to the rotation angles ofthe head of the individual with respect to the image-capturing device.

An example of a frame of reference (O1, X2, Y2, Z2) associated with theimage-capturing device is shown in FIG. 1 in the case where it is aquestion of a video camera or camera. The center O2 of this frame ofreference is for example placed in the center of the sensor of thisdevice. The axis (O2, Z2) extends along the optical axis. The axes (O2,Y2) and (O2, X2) extend in the plane perpendicular to the optical axis.

According to a second embodiment of step a), the position of the eyerotation center CRO is determined depending on a predetermined averageposition of this rotation center.

It may for example be a question of its average position with respect tothe back face of an ophthalmic lens fitted in a spectacle frame placedon the head of the individual. To this end, the rotation center may forexample be considered to be located at an average distance DM equal to27 millimeters from the back face of the ophthalmic lens. It is thuspossible to determine the position of the rotation center from acaptured two-dimensional profile image of the head of the individual(see for example FIG. 1).

According to a third embodiment of step a), the three-dimensionalcoordinates of the rotation centers of the eyes are determined fromthree-dimensional images of the head of the individual.

In the case of three-dimensional images, three-dimensionalrepresentations will also be spoken of below.

In practice, the implementation of this second embodiment is similar tothat of the first embodiment.

For example, at least two three-dimensional representations of the headof the individual are acquired while the latter fixates his gaze on atarget the position of which with respect to said first image-capturingdevice is known and for different angles of the head with respect to thefirst image-capturing device.

This first image-capturing device is here a device for acquiring thethree-dimensional representation.

The target is for example located straight in front of the individual.

For each three-dimensional representation, the position of the pupil ofthe eye of the individual is determined and the direction of the gaze isdetermined as the straight line connecting the pupil to the target.

By superposing the two representations, the rotation center of the eyeis determined as the intersection between the two determined gazedirections.

The rotation centers of the eyes of the individual may thus bepinpointed by their coordinates in a frame of reference associated withthe first device for acquiring the three-dimensional representation.

These coordinates may then be transposed to the first frame of referenceassociated with the head of the individual.

The first frame of reference may be associated with a spectacle frameplaced beforehand on the head of the individual, with particular pointsof the face of this individual, or even with a pinpointing system of thetype described in document FR2914173.

The three-dimensional representations may be obtained by a stereoscopicimage-capturing technique, or by a three-dimensional acquiring techniquesuch as a three-dimensional scanning technique, which is for examplebased on structured light.

The latter devices for acquiring a three-dimensional representationcomprise means for projecting structured light, for example including apattern such as a moire pattern, onto the head of the individual whilethe image-capturing means record one or more two-dimensional images ofthe head of the individual. Since the pattern is known, processing ofthese images allows the three-dimensional representation to bedetermined.

These three-dimensional representations may also be obtained by aplenoptic imaging method. It is a question of a multi-focal imagingmethod allowing a plurality of viewpoints to be captured with a singlesensor. This type of image (called a light-field image) allows athree-dimensional representation of the head of the individual to bedetermined.

According to a fourth embodiment of step a), the position of therotation center of the eye of the individual is determined from adatabase of morphological data of the individual.

In this case, in step a), a dataset relating to the individual and forexample originating from the processing of images or ofthree-dimensional representations recorded beforehand, is recovered andexploited by the computational processing unit to determine the positionof the rotation centers.

Generally, it is possible to envision step a) being carried out eitherby a person specialized in optometry, such as an optician, using adedicated device, or by the individual himself, without intervention bya person specialized in optometry and/or using a commonly availabledevice.

It is for example carried out at an opticians, with the dedicated meanspossessed thereby, and under the particular conditions associated withthe workplace of the optician, especially in terms of the positioning ofthe individual, lighting, measuring devices and the short time dedicatedto the measurement.

Step b)

The individual is placed in a real-life situation in which the postureof the head and body of the individual is unconstrained.

It is in particular a question of one of the following real-lifesituations:

-   -   reading and/or writing situations,    -   rest situations,    -   walking on foot situations,    -   situations in which the individual is climbing or descending a        staircase.

The reading/writing situations, in which the individual is seated on achair, stool or sofa in front of a desk, are intended to allow readingdistances and a cephalic carriage (defined by a lowering angle and aroll angle) or an angle of inclination of the head during a readingtask, to be determined.

The rest situations allow an overall bodily posture to be determined,this posture possibly influencing the vision parameters. It is inparticular important to determine whether the individual has a bent orstraight posture at rest.

A plurality of dynamic situations such as walking and climbing and/ordescending staircases for example allow oscillation or hesitationbehaviors of the individual to be observed.

In step b), the individual is preferably in his normal environment, i.e.for example in his home, at his desk, in his car or on foot in his ownneighborhood.

However, it is also possible to envision, in step b), the individualbeing in the shop of the optician. Provision may then be made forvarious real-life situations to be simulated in the shop of theoptician, the individual for example being asked to sit to read or watcha screen on a sofa or to climb or descend a staircase.

Step c)

At least one image of at least one portion of the body of the individualis captured using a second image-capturing device. It may be a questionof two- or three-dimensional images. In the case of three-dimensionalimages, three-dimensional representations will also be spoken of.

When a first device for capturing two- or three-dimensional images isused in step a), the second image-capturing device used in step c) maybe that of step a) or distinct from that of step a). The device mayoptionally be used in a different acquiring mode (multiresolution) inthe two cases.

Preferably, the two- or three-dimensional image captured in step c)comprises at least two-dimensional images

or three-dimensional representations of the head of the individual andof a portion of his chest.

Preferably, this image comprises the whole body with the head of theindividual.

According to a first embodiment of step c), said image is athree-dimensional representation of the portion of the body of theindividual.

The three-dimensional representations may be obtained, as in step a), bya stereoscopic image-capturing technique, or by a three-dimensionalacquiring technique such as a three-dimensional scanning technique,which is for example based on structured light.

The second image-capturing device is then a device for acquiring athree-dimensional representation comprising means for projectingstructured light, i.e. light having a pattern such as a moire pattern,onto the head of the individual while the image-capturing means recordone or more two-dimensional images of the head of the individual. Sincethe pattern is known, processing of these images allows thethree-dimensional representation to be determined.

A device such as the “Kinect”, the operating principle of which isdescribed in document US20100118123, may for example be used.

These three-dimensional representations may also be obtained by aplenoptic imaging method. It is a question of a multi-focal imagingmethod allowing a plurality of viewpoints to be captured with a singlesensor. This type of image (called a light-field image) allows athree-dimensional representation of the body of the individual to bedetermined.

According to a second embodiment of step c), said image captured in stepc) is a two-dimensional image captured using a second image-capturingdevice such as a camera or video camera.

Whatever the envisaged embodiment, the orientation of the individualwith respect to the second image-capturing device allows the gaze of theindividual and the environment of the individual to be observed. Forexample, in the case where the task of the individual consists inclimbing or descending staircases, it is necessary to be able to observethe posture of the head and of the body of the individual and the stairsof the staircase.

The ideal posture most often corresponds to an orientation of the bodyand head of the individual such that three quarters of the latter isseen by the second image-capturing device.

The second image-capturing device is then preferably placed such thatthe moving individual retains a substantially three-quarter orientationwith respect to this second image-capturing device in the correspondingreal-life situation.

In practice, the three-quarters posture implies that the sagittal planeof the head of the individual will be oriented at an angle comprisedbetween 20 and 50 degrees to a plane perpendicular to theimage-capturing plane of the second image-capturing device, in the casewhere a second image-capturing device captures two-capturing dimensionalimages.

Furthermore, in step c), a sequence of two- or three-dimensional imagesis preferably captured during a predetermined duration.

More precisely, at least one sequence of ten images is captured whilethe movements of the individual are unconstrained.

It is possible to envision step c) being carried out either by a personspecialized in optometry, such as an optician, using a dedicated device,or by the individual himself, without intervention by a personspecialized in optometry and/or using a commonly available device.

It is for example carried out at an opticians, with the dedicated meanspossessed thereby, and under the particular conditions associated withthe workplace of the optician, especially in terms of the positioning ofthe individual, lighting, measuring devices and the short time dedicatedto the measurement.

In practice, in order to capture the two- or three-dimensional images instep c), the individual then follows a measuring protocol announced bythe optician.

As a variant, step c) is carried out by the individual himself, in thenormal environment of the individual, using commonly available measuringdevices such as a camera, a video camera or a webcam, it then beingpossible to devote much more time thereto than is dedicated to themeasurements generally carried out at an opticians.

In practice, in order to capture the two- or three-dimensional images ofstep c), the individual then follows a measuring protocol that may beannounced by a leaflet explaining the protocol to be followed or anInternet site explaining to the individual how to carry out themeasurement. In each step of this measuring protocol, the individual maybe asked to interact with the second image-capturing device used.

Step d)

Depending on the image captured in step c), the position and orientationof said portion of the body of the individual is determined in a secondframe of reference.

This second frame of reference may be associated with said secondimage-capturing device or an absolute frame of reference, or associatedwith the environment of the individual, which is not associated with thefirst image-capturing device.

This step is carried out by the computational processing unit on thebasis of the two- or three-dimensional images captured in step c).

It is a question of determining a three-dimensional model of saidportion of the body of the individual.

Specifically, in the case where the three-dimensional representation ofthe body of the individual in step c) is acquired by virtue of a“Kinect” device 300 (FIG. 2), it is possible, as is known, to processthe three-dimensional representations acquired so as to ascertain thepositions and angles of certain segments 101, 102, 103, 104, 201, 202 ofthe body, said segments being defined beforehand by the user.

In the case of a Kinect module for example, the pinpointed segments ofthe body are defined and modelled in the OpenNI module.

On the whole, the second acquiring device gives the position andorientation of the portions of the body in space. It allows the movementof the body of the individual to be followed in real time in a quitelarge volume of space.

The resolution is about 0.5 centimeters. This resolution especiallyallows the pinpointing system placed on the head of the individual forexample to be identified.

As is schematically shown in FIG. 2, the following segments of the bodyare for example defined: the neck 101, the chest 102, the arms 103, theforearms 104, the thighs 201, the legs 202 and optionally the hands andfeet.

Each segment comprises at least one end associated with a joint of thebody and possessing at least one degree of freedom with respect to theneighboring segment.

For example, it is especially possible to take as reference system thefollowing 4 points: the left acromion (LAC), the right acromion (RAC),the manubrium (SJN) and the xiphoid process (SXS). In the case of use ofa Kinect module, the following points are for example used:SHOULDER_RIGHT, SHOULDER_LEFT, SPINE_SHOULDER, SPINE_MID.

The position of the joints of the individual and the angles of thedetermined segments allow a three-dimensional model of said portion ofthe body of the individual to be established.

In FIG. 1, the environment of the individual is schematicallyrepresented by the reference elements 500.

Step e)

The position and orientation, in the second frame of reference, of thefirst frame of reference associated with the head of the individual aredetermined by seeking the position, in the second frame of reference, ofa recognizable zone of said portion of the body of the individual, theposition and orientation of which in the first frame of reference arepredetermined.

This recognizable zone for example consists of a plurality ofrecognizable points associated with said portion of the body of theindividual.

This recognizable zone may consist of the neck of the individual.

Specifically, the neck may be visible in the image of the head of theindividual captured in step a) and in the image of the portion of thebody of the individual captured in step c).

The recognizable points of the recognizable zone may also be associatedwith the aforementioned pinpointing system mounted on the head of theindividual as mentioned above, with a spectacle frame placed on the headof the individual or with one or more recognizable points of the face ofthe individual.

Thus, preferably, in step a) the head of the individual is equipped witha pair of spectacles surmounted by a pinpointing system, in step c) thecaptured portion of the body comprises the head of the individualequipped with this pinpointing system, and in the step e) therecognizable zone consists of this pinpointing system.

The method called the “PostIt method” published by Daniel F. DeMenthonand Larry S. Davis in May 1995 may be used for this purpose. This methodallows the position and/or orientation of an object to be found from asingle two-dimensional image and a three-dimensional model of theobject.

The implementation of this method requires at least 4 points ofcorrespondence between the two-dimensional object and thethree-dimensional model to be found. These points of correspondence arefor example recognizable points of the pinpointing system placed on thehead of the individual in steps a) and c). The three-dimensional modelis that of the body of the individual and the two-dimensional objectcorresponds to the positions of the rotation center of the eye in thefirst frame of reference. The reader may for example refer to documentUS2012/321 134.

It is here in fact a question of placing the rotation centers of theeyes of the individual in the three-dimensional second frame ofreference of step c), so as to determine the position of these rotationcenters with respect to the body of the individual.

Step f)

Once the first frame of reference has been positioned with respect tothe second frame of reference, the position of the rotation center ofthe eye in said second frame of reference is determined.

It is here a question of a step of changing frame of reference.

Step g)

The parameter of visual behavior of the individual determined in step g)is for example one of the following:

-   -   a zone of use corresponding to the real-life situation of        step b) for a corrective lens to be placed in a spectacle frame        intended to equip the head of the individual,    -   a behavioral parameter of the individual specifying whether he        moves his eyes or head more during a determined visual task,    -   an average reading distance,    -   a natural posture of the individual at rest,    -   a dynamic behavior of the eyes during the chosen real-life        situation,    -   a position of a near-vision zone or progression length or inset        of a corrective lens to be placed in a spectacle frame intended        to equip the head of the individual,    -   the pantoscopic angle AMV of a corrective lens to be placed in a        spectacle frame intended to equip the head of the individual        determined so as to decrease the astigmatic aberrations.

The pantoscopic angle AMV is defined as the angle between the midplaneof each rim PMC of the spectacle frame and the vertical eye plane PVO,which is the plane perpendicular to the Frankfurt plane passing throughthe rotation centers CRO of the eyes, measured in projection in thesagittal plane of the head of the individual.

For example in step g), the direction of the gaze of the individual insaid real-life situation is determined, and a zone of use of theophthalmic lens corresponding to this real-life situation is determinedtherefrom.

The zone of use of the ophthalmic lens is defined as being a zone ofspace representative of a statistical distribution of a set of points onthe lens through which the gaze of the individual passes during aparticular visual task, or for a use at a predetermined workingdistance. The zone of use may be defined equivalently either spatially,by a statistical distribution of points over the ophthalmic lens or overanother projection plane associated with the ophthalmic lens or with therim of the corresponding frame, or vectorially, by a statisticaldistribution of directions of the gaze. Alternatively and more simply,the zone of use ZU may also be defined in tabulated format by astatistical distribution of the lowering angles of the gaze in thesagittal plane of the individual.

The lowering angle of the gaze is defined as the angle between the gazedirection and a predetermined primary gaze direction in projection inthe sagittal plane of the head of the individual.

This predetermined primary gaze direction corresponds to the gazedirection of the individual under far-vision conditions, i.e. underconditions such that the individual fixates on a point that is at adistance of at least 5 meters therefrom.

To determine the direction of the gaze of the individual, the image ofthe pupil of the individual is identified in the two- orthree-dimensional image captured in step c), and the sought direction ofthe gaze is deduced therefrom. The gaze direction is thereforedetermined depending on the position of the rotation center of the eyein the first frame of reference, which position is determined in stepa).

More precisely, this gaze direction is determined as the straight lineconnecting the rotation center of the eye and the pupil of this eye.

As a variant, an eye tracker could be used.

By virtue of step d), it is possible to define this gaze direction inthe first or second frame of reference.

It is possible to envision, to determine the direction of the gaze ofthe individual, determining the position, in the second frame ofreference, of elements targeted by the gaze and belonging to theenvironment of the individual. The elements targeted by the gaze inquestion are for example displayed on a display screen and have a knownposition with respect to the second image-capturing device.

These targeted elements may thus consist of a display screen, staircasestairs, the pages of a book, or any element of the environment of theindividual.

The direction of the gaze may then be determined as the straight lineconnecting the rotation center of the eye and the targeted elementfixated on by the gaze of the individual.

Next, the intersection of the direction of the gaze and a midplane ofthe ophthalmic lens, which is intended to be placed in front of the eyeof the individual, is for example determined.

The midplane of the ophthalmic lens may optionally be approximated bythe midplane of the rim of the corresponding frame.

The position and orientation of the midplane of the lens are for examplepredetermined in a calibrating step.

This determination may take into account the shape of the spectacleframe chosen by the individual. To replace the midplane of the lens, itis also possible to use the front or back face of the lens, or amid-surface equidistant from this front and back face.

In the case where the ophthalmic lens in question is a progressive lens,the determined zone of use may in particular consist of the near- orfar-vision zone of the progressive ophthalmic lens.

The power of the progressive ophthalmic lens varies, preferablycontinuously, between a far-vision reference point located in the zoneof use of the lens used for far vision and a near-vision reference pointlocated in the zone of use used for near vision, along a curve calledthe “principal progression meridian curve” that passes between these twopoints. This principal progression meridian curve passes through thesetwo zones of use and an intermediate zone of use located between thezone of near-vision use and the zone of far-vision use, in an overallvertical direction.

The progression length and/or the inset of the progressive ophthalmiclens may also advantageously be deduced depending on this zone of near-and/or far-vision use.

The progression length of the ophthalmic lens is defined as the verticaldistance between the fitting cross and the position of the near-visionreference point defined by the manufacturer of the eyeglass.

The fitting cross is a reference point for positioning the lens in frontof the eye of an individual and the position of which is predefined bythe manufacturer of the lens.

Other definitions may be adopted for the progression length. It may beexpressed relative to the prism reference point or to the far-visionreference point rather than relative to the fitting cross. As therespective positions of these points are moreover also given by themanufacturer, this definition is equivalent to the preceding one.

The inset of the progressive ophthalmic lens is defined as thehorizontal shift between the far-vision reference point and thenear-vision reference point. The inset E is also called “internaloffset”.

The behavioral parameter of the individual specifying whether he moveshis eyes or his head more during a determined visual task may forexample be an eye-head coefficient defined by the ratio of the amplitudeof the movement of an eye of the individual in a determined direction ina determined visual situation to the maximum theoretical amplitude ofthe movement of this eye in this visual situation.

This behavioral parameter may also comprise an amplitude of the movementof at least one eye of the individual and/or an amplitude of themovement of the head of the individual in this determined visualsituation.

The determined visual situation may in particular correspond to areading task.

The eye-head coefficient then for example corresponds to the ratio ofthe angular amplitude of the movement of the eye of the individual whilehe is reading a predetermined text to the maximum theoretical amplitudeof this movement depending on the width of the text displayed and thereading distance of the individual.

It is possible to compare in the same way the angular amplitude of themovement of the head of the individual while he is reading and themaximum theoretical amplitude of this movement.

Moreover, the average reading distance may be obtained by processing theimages obtained in step c), by identifying in these images the image ofthe reading medium, which belongs to the environment of the individual.It is for example defined as the distance between the rotation centersof the eyes and this reading medium.

The natural posture of the individual at rest corresponds to theposition and orientation of the head and of at least said portion of thebody of the individual when the latter is not carrying out a particularvisual task.

The dynamic behavior of the eyes during the chosen real-life situationis determined using a statistical treatment of the images obtained instep c).

For this purpose a sequence of two- or three-dimensional images iscaptured in step c) during a predetermined duration. More precisely, atleast one sequence of ten images is captured while the movements of theindividual are unconstrained.

It is thus possible to deduce therefrom the variation in the soughtparameter of visual behavior during this predetermined duration.

The pantoscopic angle of a corrective ophthalmic lens to be placed in aspectacle frame intended to equip the head of the individual isdetermined so as to decrease the astigmatic aberrations.

Generally, whatever the details of the envisioned implementation, asmentioned above, steps a) and c) may be carried out in the same place,using the same image-capturing device, or in two different places, usingtwo different image-capturing devices.

Preferably, at least steps b) and c) are carried out by the individualin his normal environment.

It is for example envisioned that the normal environment of the userwill comprise a working environment, for example a desk; a homeenvironment, for example a sofa placed in front of a television set oran easy chair for reading; and an automobile environment, for example adashboard equipped with a steering wheel.

The normal environment of the individual also comprises a portion of theneighborhood in which the individual lives.

In the case where it is envisioned to carry out steps a) and c) in thesame place, for example the shop of an optician, it is possible forexample to envision the first and second image-capturing devices beingincorporated into a measuring column located in the shop of theoptician.

The column then for example incorporates a device for capturingtwo-dimensional images, such as a video camera, and a device forcapturing three-dimensional images, such as a Kinect or 3D scanner. Thetwo devices may also be combined into a single acquiring system forexample using the Ray-light technology.

The device for capturing three-dimensional images may optionally becontrolled remotely via a remote control by the optician in order toallow suitable images to be captured in the shop environment, forexample while the individual is walking to or reading at one of thedispensing desks thereof.

It is also possible to envision studied placement of a plurality ofimage-capturing devices, in order to cover the shop environment in itsentirety. By way of example, the Kinect has a range of 8 meters over asolid angle of about 60 degrees. It is therefore possible to plan outthe places observed by these devices.

It is also possible to envision the first image-capturing device beingincorporated into a measuring column, whereas the second image-capturingdevice comprises a portable device that the optician or individualbrings into the shop.

In the case where it is envisioned to carry out steps a) and c) in twodifferent places, for example on the one hand in the shop of an opticianand on the other hand in the home of the individual, it is for examplepossible to envision the first image-capturing device being incorporatedinto a measuring column located in the shop of the optician and toenvision the second image-capturing device being incorporated into awidely available device, that the individual has access to in his home,and which is preferably connectable to the Internet.

In this case, the second measuring device, a Kinect or tablet forexample, is connected via an Internet site to the computationalprocessing unit. The individual may identify himself on this site usingan identifier and obtain help with the implementation of step c) of themethod, for example with the placement of the capturing device, thetests to be carried out before images are captured, etc.

This may be carried out before or after a piece of optical equipment hasbeen sold.

The parameters of visual behavior are used to personalize the ophthalmiclenses intended for the individual. They allow a standard ophthalmiclens to be modified in order to make it match as best as possible theneeds of the individual. It is also possible to weight behavioralparameters already determined at the opticians.

1. A method for determining at least one parameter of visual behavior ofan individual, comprising the following steps: determining the positionof the rotation center (CRO) of at least one eye (OD) of the individualin a first frame of reference associated with the head of theindividual, capturing, using an image-capturing device, at least oneimage of at least one portion of the body of the individual in a secondframe of reference, determining the position and orientation, in thesecond frame of reference, of the first frame of reference associatedwith the head (TS) of the individual, by seeking the position, in thesecond frame of reference, of a recognizable zone of said portion of thebody of the individual, determining the position of the rotation center(CRO) of the eye in the second frame of reference, determining thesought parameter of visual behavior.
 2. The method as claimed in claim1, wherein, for the capturing step, the individual is placed in areal-life situation in which the posture of the head (TS) and body ofthe individual is unconstrained.
 3. The method as claimed in claim 1,wherein the position and orientation of the recognizable zone of saidportion of the body of the individual are predetermined in the firstframe of reference.
 4. The method as claimed in claim 1, wherein, in thestep of determining the position of the rotation center in the firstframe of reference, the position of the rotation center (CRO) of the eyeof the individual is determined from a morphological database of theindividual.
 5. The method as claimed in claim 1, wherein, in the step ofdetermining the position of the rotation center in the first frame ofreference, the position of the rotation center (CRO) of the eye of theindividual is determined from one or more acquisitions of images of thehead (TS) of the individual.
 6. The method as claimed in claim 1,wherein, in the capturing step, said image is a three-dimensionalrepresentation of the portion of the body of the individual.
 7. Themethod as claimed in claim 1, wherein, in the capturing step, said imageis a three-dimensional representation of the head of the individual. 8.The method as claimed in claim 1, wherein, in the capturing step, asequence of images is captured during a predetermined duration, and, inthe step of determining the sought parameter of visual behavior, thevariation in the sought parameter of visual behavior during thispredetermined duration is deduced therefrom.
 9. The method as claimed inclaim 1, wherein, in the step of determining position and orientation,said recognizable zone consists of a pinpointing system mounted on thehead (TS) of the individual, of a spectacle frame (10) placed on thehead (TS) or of one or more recognizable points of the face of theindividual.
 10. The method as claimed in claim 1, wherein, in the stepof determining the parameter of visual behavior, the direction of thegaze of the individual in said real-life situation is determined, and azone of use of the ophthalmic lens corresponding to this real-lifesituation is determined therefrom.
 11. The method as claimed in claim10, wherein, to determine the direction of the gaze of the individual,the image of the pupil of the individual is identified in the imagecaptured in the capturing step, and the sought direction of the gaze isdeduced therefrom depending on the position of the rotation center (CRO)in the first frame of reference, said position being determined in thestep of determining the position of the rotation center in the firstframe of reference.
 12. The method as claimed in claim 10, wherein, todetermine the direction of the gaze of the individual, the position inthe second frame of reference of elements targeted by the gaze andbelonging to the environment of the individual is determined.
 13. Themethod as claimed in claim 12, wherein, said elements targeted by thegaze are displayed on an electronic screen and have a known positionwith respect to the image-capturing device.
 14. The method as claimed inclaim 1, wherein, in the step of determining the position of therotation center in the first frame of reference, at least two images ofthe head (TS) of the individual are captured using an image-capturingdevice, in which images the postures of the head (TS) of the individualwith respect to this image-capturing device are different and in whichimages the individual is fixating his gaze on a sighting point ofpredetermined position, the gaze directions of the individualcorresponding to each of the two images are determined, the position ofthe rotation center (CRO) of the eye of the individual is deducedtherefrom.
 15. The method as claimed in claim 1, wherein, in the step ofdetermining the position of the rotation center in the first frame ofreference, the head (TS) of the individual is equipped with a pair ofspectacles surmounted by a pinpointing system, in the capturing step,the captured portion of the body comprises the head (TS) of theindividual equipped with this pinpointing system, and, in the step ofdetermining the position and orientation, the recognizable zone consistsof this pinpointing system.
 16. The method as claimed in claim 1,wherein the sought parameter of visual behavior of the individual is oneof the following: a zone of use corresponding to the real-life situationof step b) for a corrective lens to be placed in a spectacle frame (10)intended to equip the head of the individual, a behavioral parameter ofthe individual specifying whether he moves his eyes or head (TS) more,average reading distance, natural posture of the individual at rest,dynamic behavior of the eyes during the chosen real-life situation,position of a near-vision zone or progression length or inset of acorrective lens to be placed in a spectacle frame (10) intended to equipthe head (TS) of the individual, the pantoscopic angle of a correctivelens to be placed in a spectacle frame (10) intended to equip the head(TS) of the individual determined so as to decrease the astigmaticaberrations.
 17. The method as claimed in claim 1, wherein the steps ofdetermining the position of the rotation center in the first frame ofreference and of capturing are carried out in one and the same place,using one and the same image-capturing device.
 18. The method as claimedin claim 1, wherein the steps of determining the position of therotation center in the first frame of reference and of capturing arecarried out in two different places, using two different image-capturingdevices.
 19. The method as claimed in claim 2, wherein the position andorientation of the recognizable zone of said portion of the body of theindividual are predetermined in the first frame of reference.
 20. Themethod as claimed in claim 2, wherein, in the step of determining theposition of the rotation center in the first frame of reference, theposition of the rotation center (CRO) of the eye of the individual isdetermined from a morphological database of the individual.